1. Field of the Invention
The present invention relates to a method for pattern formation wherein a fine pattern used in fields such as semiconductor device and the like is formed. The present invention relates also to a chemically amplified resist used in pattern formation, a polymer useful for obtaining this resist composition, and a novel compound as a raw material for the polymer.
2. Description of the Related Art
In production of various electronic devices represented by semiconductor device, requiring microfabrication of half-micron order, demands for higher integration density and higher integration level of such devices are growing. Therefore, the requirement for the photolithography used for fine pattern formation is becoming increasingly severe. In production of, in particular, a DRAM having an integration level of 1 G bits or more wherein a processing technique of 0.13 xcexcm or less is required, a photolithography using an ArF excimer laser (193 nm) is going to be utilized. In formation of an even finer pattern, utilization of a photolithography using a F2 excimer laser (157 nm) has been considered recently (R. R. Kunz et al., Journal of Vacuum Science and Technology, Vol. B17 (No. 6), pp. 3267-3272 (1999)).
Hence, it is desired to develop a resist material corresponding to the photolithography by F2 excimer laser beam. In developing a resist to be exposed to the F2 excimer laser beam, the cost performance of laser must be improved because the gas as a raw material for the laser has a short life and the laser equipment is expensive. Therefore, a high resolution corresponding to finer pattern forming and a high sensitivity are strongly required for the resist. As the method for allowing a resist to have a high sensitivity, it is well known to use a chemically amplified resist using a photo acid generator as a sensitizer. As a typical example of such a chemically amplified resist, there is described, in JP-B-2-27660, a resist consisting of a combination of triphenylsulfonium hexafluoroarsenate and a poly (p-tert-butoxycarbonyloxy-xcex1-methylstyrene). Such a chemically amplified resist is currently in wide use as a resist for KrF excimer laser (248 nm) (for example, Hiroshi Ito and C. Grant Wilson, American Chemical Society Symposium Series, Vol. 242, pp. 11-23 (1984)). The feature of the chemically amplified resist lies in that the photo acid generator contained as a component generates a protonic acid when exposed to a light and, in the heat treatment after light exposure, the acid gives rise to an acid-catalyzed reaction with the resist resin, etc. In this way is achieved a sensitivity far higher than those of conventional resists whose photoreaction efficiency (the reaction per one photon) are less than 1. Most of the resists developed recently are chemically amplified type.
In the lithography using a light having a short wavelength of 180 nm or less typified by a F2 excimer laser beam, however, the resist used therein for formation of a fine pattern needs to have a new property not exhibited by conventional materials, i.e. a transparency to a light of 180 nm or less to be applied.
In conventional resist materials for KrF excimer laser and ArF excimer laser, there are mostly used, as the resin component, a poly(p-vinylphenol), an alicyclic resin, etc. These resins, however, show very strong absorption to a light of 180 nm or less wavelength. Therefore, the most part of the light applied is absorbed at the surface of such a resist and the light applied does not reach a substrate on which the resist is coated, making it impossible to form a fine resist pattern. For this reason, it is impossible to use a conventional resin in a photolithography using a light of short wavelength of 180 nm or less. Hence, a resist resin transparent to a wavelength of 180 nm or less is desired strongly.
As the polymer compound having transparency to a F2 excimer laser beam (157 nm), fluorine-containing resins are considered to be promising (R. R. Kunz et al., Journal of Vacuum Science and Technology, Vol. B17 (No. 6), pp. 3267-3272 (1999), and T. M. Bloomstein et al., Journal of Vacuum Science and Technology, Vol. B16 (No. 6), pp. 3154-3157 (1998)).
Conventional fluorine-containing resins typified by polytetrafluoroethylene, however, have no functional group such as to give rise to a chemical reaction by the action of an acid, resulting in a change in solubility in alkali developing solution and further have no polar group (resultantly have low adhesivity to substrate); therefore, can not be used as a resin for chemically amplified resist.
Hence, a new resin material for resist usable in a lithography using a light of 180 nm or less is desired strongly.
It is an object of the present invention to provide a chemically amplified resist composition which can be suitably used in a lithography using a light of 180 nm or less wavelength, which enables formation of a fine pattern. It is also an object of the present invention to provide a polymer suitable for obtaining the above resist composition, a novel compound suitable as a raw material for the polymer, and a method for pattern formation capable of forming a fine pattern using the above resist composition.
The present invention lies in a fluorine-containing phenylmaleimide derivative represented by the general formula (1). 
(In the formula (1), one of R1, R2, R3, R4 and R5 is a hydroxy group, an alkoxyl group, or an acid-dissociable organic group of 20 or less carbon atoms capable of generating a hydroxy group when decomposed by an acid; at least two of the remainder are each a fluorine atom; and when there is still a remainder, it is a hydrogen atom.)
The present invention lies also in a polymer characterized by being obtained by polymerizing monomers containing the above fluorine-containing phenylmaleimide derivative.
The present invention lies further in a polymer characterized by containing at least a structural unit represented by the general formula (2) and having a weight-average molecular weight of 2,000 to 200,000. 
(In the formula (2), one of R1, R2, R3, R4 and R5 is a hydroxy group, an alkoxyl group, or an acid-dissociable organic group of 20 or less carbon atoms capable of generating a hydroxy group when decomposed by an acid; at least two of the remainder are each a fluorine atom; and when there is still a remainder, it is a hydrogen atom.)
Preferably, the polymer contains, in addition to the structural unit represented by the general formula (2), a structural unit represented by the following general formula (3). 
(In the above formula, R6, R7, R8 and R9 are each independently a hydrogen atom, a fluorine atom, a trifluoromethyl group, a hydroxy group, a hydroxyalkyl group, a 1,1,1,3,3,3-hexafluoro-2-hydroxyisopropyl group, a 1,1,1-trifluoro-2-trifluoromethyl-2-hydroxypropyl group, an acid-dissociable organic group of 20 or less carbon atoms capable of generating a 1,1,1,3,3,3-hexafluoro-2-hydroxyisopropyl group when decomposed by an acid, an acid-dissociable organic group of 20 or less carbon atoms capable of generating a 1,1,1-trifluoro-2-trifluoromethyl-2-hydroxypropyl group when decomposed by an acid, or an acid-dissociable organic group of 20 or less carbon atoms capable of generating a carboxy group when decomposed by an acid.)
Preferably, these polymers are a copolymer which contains, in addition to the structural unit represented by the general formula (2), at least one kind of other structural unit and wherein the proportion of the structural unit represented by the general formula (2) in the total structural units of the copolymer is 5 to 90 mole %.
The present invention further includes a chemically amplified resist composition characterized by containing at least the above polymer and a photo acid generator capable of generating an acid when exposed to a light and also characterized in that the proportion of the polymer to the total mass of the polymer and the photo acid generator is 70 to 99.8% by mass and the proportion of the photo acid generator to the total mass of the polymer and the photo acid generator is 0.2 to 30% by mass.
The present invention includes also a method for pattern formation, characterized by comprising at least
a step of coating the above chemically amplified resist composition on a to-be-processed substrate,
a step of exposing using a light of 180 nm or less wavelength,
a step of conducting baking, and
a step of conducting development.
In the method, the light for the exposure is preferably a light of 120 to 180 nm wavelength. Also, the light for the exposure is preferably a F2 excimer laser beam.
In the general formula (1) and the general formula (2), one of R1, R2, R3, R4 and R5 is a hydroxy group, an alkoxyl group, or an acid-dissociable organic group of 20 or less carbon atoms capable of generating a hydroxy group when decomposed by an acid; at least two of the remainder are each a fluorine atom; and when there is still a remainder, it is a hydrogen atom. That is, one of the five groups of R1 to R5 is a hydroxy group, an alkoxyl group, or an acid-dissociable organic group of 20 or less carbon atoms capable of generating a hydroxy group when decomposed by an acid; as to the remaining four groups, all of the four groups are a fluorine atom, or three groups thereof are a fluorine atom and other one group is a hydrogen atom, or two groups thereof are a fluorine atom and other two groups are a hydrogen atom.
As preferable specific examples of the alkoxyl group, there can be mentioned methoxy group, ethoxy group, n-propoxy group, n-butoxy group, n-pentyloxy group, n-hexyloxy group, n-heptyloxy group, n-octyloxy group and n-nonyloxy group. The alkoxy group can be other group.
As preferable specific examples of the acid-dissociable organic group of 20 or less carbon atoms capable of generating a hydroxy group when decomposed by an acid, there can be mentioned t-butoxy group, tetrahydropyranyloxy group, tetrahydrofuranyloxy group, 1-methoxyethoxy group, 1-ethoxyethoxy group, 1-propoxyethoxy group, 1-butoxyethoxy group, methoxyethoxymethoxy group, methoxymethoxy group and t-butoxycarbonyloxy group. The acid-dissociable organic group can be other group.
The polymer of the present invention may be a polymer obtained by polymerizing a maleimide derivative represented by the general formula (1), or may be a copolymer obtained by copolymerizing a maleimide derivative represented by the general formula (1) and other polymerizable compound.
As a preferable specific example of the copolymer, there can be mentioned a polymer containing, in addition to a structural unit represented by the general formula (2), a structural unit represented by the following general formula (3). However, the copolymer can be other polymer. 
(In the above formula, R6, R7, R8 and R9 are each independently a hydrogen atom, a fluorine atom, a trifluoromethyl group, a hydroxy group, a hydroxyalkyl group, a 1,1,1,3,3,3-hexafluoro-2-hydroxyisopropyl group, a 1,1,1-trifluoro-2-trifluoromethyl-2-hydroxypropyl group, an acid-dissociable organic group of 20 or less carbon atoms capable of generating a 1,1,1,3,3,3-hexafluoro-2-hydroxyisopropyl group when decomposed by an acid, an acid-dissociable organic group of 20 or less carbon atoms capable of generating a 1,1,1-trifluoro-2-trifluoromethyl-2-hydroxypropyl group when decomposed by an acid, or an acid-dissociable organic group of 20 or less carbon atoms capable of generating a carboxy group when decomposed by an acid.)
As preferable specific examples of the acid-dissociable organic group of 20 or less carbon atoms capable of generating a 1,1,1,3,3,3-hexafluoro-2-hydroxyisopropyl group when decomposed by an acid, there can be mentioned 1,1,1,3,3,3-hexafluoro-2-t-butoxyisopropyl group, 1,1,1,3,3,3-hexafluoro-2-t-butoxycarbonyloxyisopropyl group, 1,1,1,3,3,3-hexafluoro-2-tetrahydropyranyloxyisopropyl group, 1,1,1,3,3,3-hexafluoro-2-(1-ethoxyethoxy)isopropyl group, 1,1,1,3,3,3-hexafluoro-2-(1-butoxyethoxy)isopropyl group, 1,1,1,3,3,3-hexafluoro -2-tetrahydrofuranyloxyisopropyl group, 1,1,1,3,3,3-hexafluoro-2-(1-methoxyethoxy)isopropyl group, 1,1,1,3,3,3-hexafluoro-2-(1-propoxyethoxy)isopropyl group, 1,1,1,3,3,3-hexafluoro-2-(methoxyethoxymethoxy)isopropyl group, and 1,1,1,3,3,3-hexafluoro-2-(methoxymethoxy)isopropyl group. However, the acid-dissociable organic group can be a group other than the above groups.
As preferable specific examples of the acid-dissociable organic group of 20 or less carbon atoms capable of generating a 1,1,1-trifluoro-2-trifluoromethyl-2-hydroxypropyl group when decomposed by an acid, there can be mentioned 1,1,1-trifluoro-2-trifluoromethyl-2-t-butoxypropyl group, 1,1,1-trifluoro-2-trifluoromethyl-2-t-butoxycarbonyloxypropyl group, 1,1,1-trifluoro-2-trifluoromethyl-2-tetrahydropyranyloxypropyl group, 1,1,1-trifluoro-2-trifluoromethyl-2-(1-ethoxyethoxy)propyl group, 1,1,1-trifluoro-2-trifluoromethyl-2-(1-butoxyethoxy)propyl group, 1,1,1-trifluoro-2-trifluoromethyl-2-tetrahydrofuranyloxypropyl group, 1,1,1-trifluoro-2-trifluoromethyl-2-(1-methoxyethoxy)propyl group, 1,1,1-trifluoro-2-trifluoromethyl-2-(1-propxyethoxy)propyl group, 1,1,1-trifluoro-2-trifluoromethyl-2-(methoxyethoxymethoxy)propyl group, and 1,1,1-trifluoro-2-trifluoromethyl-2-(methoxymethoxy)propyl group. However, the acid-dissociable organic group can be a group other than the above groups.
As preferable specific examples of the acid-dissociable organic group of 20 or less carbon atoms capable of generating a carboxy group when decomposed by an acid, there can be mentioned t-butoxycarbonyl group, tetrahydropyranyloxycarbonyl group, tetrahydrofuranyloxycarbonyl group, ethoxyethyloxycarbonyl group, butoxyethyloxycarbonyl group, methoxyethyloxycarbonyl group and methoxyethoxyethyloxycarbonyl group. However, the acid-dissociable organic group can be a group other than the above groups.
Also, the polymer having a structural unit represented by the general formula (2) may contain, in addition to a structural unit represented by the general formula (3), other copolymerizable structural unit. Or, it is possible that the polymer having a structural unit represented by the general formula (2) contains no structural unit represented by the general formula (3) and contains other structural unit.
As the other copolymerizable monomer used for obtaining the above other structural unit, there can be mentioned, for example, (meth)acrylic acid; aliphatic esters of (meth)acrylic acid, such as methyl (meth)acrylate, ethyl (meth)acrylate and the like; alicyclic esters of (meth)acrylic acid, such as adamantyl (meth)acrylate, tricyclodecyl (meth)acrylate, tetracyclododecyl (meth)acrylate, norbornyl (meth)acrylate, isobornyl (meth)acrylate and the like; substituted or unsubstituted tetracyclododecyl derivatives (there can be mentioned, for example, 3-tetracyclo [4.4.0.12,5.17,10]dodecene-8-carboxylic acid, 3-tetracyclo[4.4.0.12,5.17,10]dodecene-8-ol, 3-tetracyclo[4.4.0.12,5.17,10]dodecene-8-methanol, t-butyl 3-tetracyclo[4.4.0.12,5.17,10]dodecene-8-carboxylate and 3-tetracyclo[4.4.0.12,5.17,10]dodecene); vinyl ethers (there can be mentioned, for example, ethyl vinyl ether, isobutyl vinyl ether, 2-vinyloxyethoxybenzene, and 1,2,3,4,5-pentafluoro-6-(2-vinyloxyethoxy)benzene); fluorine-containing styrene derivatives (there can be mentioned, for example, trifluoromethylstyrene, pentafluorostyrene, xcex1, xcex2, xcex2-trifluorostyrene and xcex2, xcex2-difluorostyrene); fluoroethylenes such as tetrafluoroethylene and the like. Other monomer can be used as well.
The proportion of the structural unit represented by the general formula (2) in the total structural units of the copolymer is preferably 5 mole % or more, more preferably 10 mole % or more. Meanwhile, it is preferably 100 mole % or less, more preferably 90 mole % or less. The reason is that when the proportion of the structural unit represented by the general formula (2) is 5 mole % or more, the resin is superior in transparency and resolution characteristics.
The polymer of the present invention can be produced by an ordinary polymerization process such as radical polymerization, anionic polymerization or the like. The radical polymerization is carried out, for example, by adding an appropriate radical polymerization initiator (for example, azobisisobutyronitrile) in dry tetrahydrofuran or toluene in an inert gas (for example, argon or nitrogen) atmosphere and stirring the resulting mixture at 50 to 100xc2x0 C. for 0.5 to 50 hours. The anionic polymerization is carried out, for example, by adding an appropriate anionic polymerization initiator (for example, n-butyllithium, sec-butyllithium or potassium t-butoxide) in dry tetrahydrofuran in an inert gas (for example, argon or nitrogen) atmosphere and stirring the resulting mixture at xe2x88x9278 to 0xc2x0 C. for 0.5 to 24 hours.
The weight-average molecular weight of the polymer is preferably 2,000 to 200,000. It is because when the molecular weight is 2,000 or more, formation of resist film is easy and, when the molecular weight is 200,000 or less, the resin is superior in solubility in solvent and resolution characteristics.
The chemically amplified resist composition of the present invention contains at least the polymer of the present invention and a photo acid generator and may further contain a solvent as necessary.
The photo acid generator used in the present invention is desirably a photo acid generator which generates an acid when exposed to a light of 180 nm or less, more preferably 120 to 180 nm. The photo acid generator can be appropriately selected from such photo acid generators as its mixture with the above-mentioned polymer of the present invention, etc. is sufficiently soluble in the organic solvent used and the resulting solution can form a uniform film when coated by spin coating or the like. The photo acid generator can be used singly or in admixture of two or more kinds.
As examples of the photo acid generator usable, there are triphenylsulfonium salt derivatives by J. V. Crivello et al. described in Journal of the Organic Chemistry, Vol. 43, No. 15, pp. 3055 to 3058 (1978); other onium salts represented thereby (for example, compounds such as sulfonium salt, iodonium salt, phosphonium salt, diazonium salt, ammonium salt and the like); 2,6-dinitrobenzyl esters (O. Nalamasu et al., SPIE Proceeding, Vol. 2195, p. 137 (1994)); 1,2,3-tri(methanesulfonyloxy)benzene (Takumi Ueno et al., Proceeding of PME ""89, Kodansha, pp. 413 to 424 (1990)); and sulfosuccinimides disclosed in JP-A-5-134416.
The content of the photo acid generator is preferably 0.2% by mass or more, more preferably 1% by mass or more relative to the total of the polymer and the photo acid generator in order to allow the resulting chemically amplified resist composition to have a sufficient sensitivity and form a good pattern. Meanwhile, the content is preferably 30% by mass or less, more preferably 15% by mass or less in order to form a uniform film and suppress the generation of scum after development.
For the same reasons, the content of the polymer is preferably 70 to 99.8% by mass relative to the total of the polymer and the photo acid generator.
The chemically amplified resist composition of the present invention is ordinarily produced in the form of a resist solution by dissolving the components such as polymer, photo acid generator and the like in an appropriate solvent and is coated on a to-be-processed substrate by spin coating or the like.
As to the solvent, there is no particular restriction as long as it is such an organic solvent as components such as polymer, photo acid generator and the like are sufficiently soluble therein and the resulting solution can form a uniform film by spin coating or the like. The solvent can be used singly or in admixture of two or more kinds. As the solvent, there can be specifically mentioned n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, tert-butyl alcohol, methyl cellosolve acetate, ethyl cellosolve acetate, propylene glycol monoethyl ether acetate, propylene glycol monomethyl ether acetate, methyl lactate, ethyl lactate, 2-methoxybutyl acetate, 2-ethoxyethyl acetate, methyl pyruvate, ethyl pyruvate, methyl 3-methoxypropionate, ethyl 3-methoxypropionate, N-methyl-2-pyrrolidinone, cyclohexanone, cyclopentanone, cyclohexanol, methyl ethyl ketone, 1,4-dioxane, ethylene glycol monomethyl ether, ethylene glycol monomethyl ether acetate, ethylene glycol monoethyl ether, ethylene glycol monoisopropyl ether, diethylene glycol monomethyl ether, diethylene glycol dimethyl ether, etc. Other solvent can be used as well.
The xe2x80x9cbasicxe2x80x9d components of the chemically amplified resist composition of the present invention is the above-mentioned resin, photo acid generator and solvent. Other components such as dissolution inhibitor, surfactant, pigment, stabilizer, coatability improver, dye and the like can be added as necessary to produce the chemically amplified resist.
The chemically amplified resist composition of the present invention is coated on a to-be-processed substrate; to the resulting material is exposed with a light having a wavelength of 180 nm or less, preferably 120 to 180 nm; baking is conducted; development is conducted; thereby, a pattern can be formed.
The light for the exposure is preferably a F2 excimer laser beam.
The present invention is described below in more detail by way of Examples. However, the Examples restrict the present invention in no way. Incidentally, as to the reagents, etc., commercial high-purity products were used in the following unless otherwise specified.